This project aims to investigate specific speech perception problems of elderly listeners and without hearing impairment in ideal and noisy environments, and to determine whether stimulus modification techniques via digital editing effectively enhance the speech signal for these subjects. Rather than using lexical items that are typically analyzed for total percent correct, nonsense syllable stimuli will be presented to identify specific acoustic and phonetic features that are poorly perceived by the elderly. Further, discrete modifications of poorly perceived features will be employed, rather than previous techniques of transforming the entire signal. Testing of human subjects prior to and following each acoustic modification will be conducted to evaluate the effectiveness of each stimulus enhancement technique in a variety of listening environments.